1. Field of the Invention
The present invention relates generally to a radio paging receiver. More specifically, the invention relates to a battery saving function for reducing power consumption in a radio paging receiver.
2. Description of the Related Art
A radio paging receiver receives a radio paging signal from a base station of a paging system, by means of an antenna. After amplification of the radio paging signal at a radio reception portion, the radio paging signal is subject to frequency mixing with a local oscillation signal from a local oscillator portion employing a quartz oscillator as a source oscillator to obtain a low frequency signal. The low frequency signal is binary-coded by a wave shaper circuit and thus converted into a digital signal. The paging signal containing the digital signal is compared with its own paging number stored in a ROM by a decoder. When a match is established, the decoder drives a ring drive circuit by a paging notice signal to generate a ring sound through a speaker to notice the user of reception of a page.
When a display message is transmitted following to the foregoing paging signal, the decoder drives a display driver portion for displaying the message on a display portion after decoding the message. This type of selective radio paging receiver permits checking of the received message by depression of a reset switch.
Such a selective radio paging receiver employs a battery as a primary power source. Also, it is possible to produce a secondary power source from the battery to provide a power supply to the foregoing circuit from the primary and secondary power sources, if required. Accordingly, in this type of selective radio paging receiver, for expanding the life of the battery for convenience of the user, it is necessary to conserve the battery supply by reducing power consumption.
Most of the battery conservation found in conventional radio paging receivers supplies power at a predetermined voltage for the radio reception portion, including local oscillator portion, wave shaper circuit and so forth, which consume large power, intermittently (e.g. Japanese Unexamined Patent Publications (Kokai) Nos. Showa 61-92050 and Showa 58-182332). Also, another type of battery conservation is to lower an operation voltage in a specific circuit except for normal operation state to reduce power consumption (e.g. Japanese Unexamined Patent Publications Nos. Heisei 4-342320, Heisei 3-248635, Heisei 2-58936).
The conventional selective radio paging receiver set forth above intermittently supplies power to the circuit consuming large amounts of power, such as radio reception portion including the local oscillator, wave shaper circuit and so forth, or supplies lowered supply voltage except for normal operation state. In such case, the timing of battery saving operation has to be determined with taking resume period required to resume normal oscillating condition of the quartz oscillator in the local oscillator, into account. However, in the conventional receiver, battery saving operation is performed at the timing adapted to the rise period of the local oscillator even for the radio reception portion, wave shaper circuit and so forth, which are quick in resumption of normal operation. As a result, power consumption can not be reduced satisfactorily.
Also, since the quartz oscillator requires longer period to resume normal oscillation under low temperature environment, the selective radio paging receiver is required to set further long period of power supply for the local oscillator portion to further degrade effect of battery saving. It should be appreciated that the period required to resume normal operation of the quartz oscillator becomes longer at lower operation voltage. Therefore, when the operation voltage is low, the required period becomes further longer.